STOICHIOMETRY ANALOGY

Chemistry 65

Chapter 8

STOICHIOMETRY ANALOGY

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Stoichiometry is the quantitative relationship between the reactants and products in a

balanced chemical equation. Stoichiometry allows chemists to predict how much of a

reactant is necessary to form a given amount of product or how much of a reactant is

required to completely react with another reactant.

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The concept of stoichiometry is analogous to the concept of a recipe such as the one

shown below:

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Much like a chemical equation, the recipe above shows the numerical relationship

between the ingredients (reactants) and the pancakes (products).

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For example, since 2 eggs are required to make 5 pancakes, it would follow that 8 eggs

would be required to make 20 pancakes.

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Much like a chemical equation, the recipe contains numerical relationships between the

pancake ingredients and the number of pancakes. Some other relationships are shown

below:

1 cup flour = 5 pancakes

? tsp baking powder = 5 pancakes

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Chemistry 65

Chapter 8

STOICHIOMETRY

?

A balanced chemical equation provides several important information about the reactants

and products in a chemical reaction. For example:

1N2(g)

+

3 H2(g)

2 NH3(g)

1 molecule

3 molecules

100 molecules

300 molecules

1 million molecules 3 million molecules

1 mole N2

+

2 molecules

200 molecules

2 million molecules

3 moles H2

2 moles NH3

This is the MOLE RATIO between REACTANTS and PRODUCTS

Summary of Stoichiometric Calculations in Chemistry

Examples:

1. Determine each mole ration based on the reaction shown below:

2 C4H10 + 13 O2 ¡ú 8 CO2 + 10 H2O

a)

mol O2

=

mol CO2

b)

2

mol C4 H10

=

mol H2O

Chemistry 65

Chapter 8

STOICHIOMETRIC CALCULATIONS

Mole-Mole Calculations:

? Relates moles of reactants and products in a balanced chemical equation

Examples:

1. How many moles of nitrogen will react with 2.4 moles of hydrogen to produce ammonia

as shown in the reaction below?

1

N2(g) + 3 H2(g)

2.4 mol H2 x

2 NH3(g)

1 mol N2

= 0.80 mol N2

3 mol H2

Mole Ratio

2. How many moles of ammonia can be produced from 32 moles of hydrogen?

(Assume excess nitrogen present)

32 mol H2 x ????? =

mol NH3

3. In one experiment, 6.80 mol of ammonia are prepared. How many moles of hydrogen

were used up in this experiment?

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Chemistry 65

Chapter 8

STOICHIOMETRIC CALCULATIONS

Mass-Mole Calculations:

? Relates moles and mass of reactants or products in a balanced chemical equation

Examples:

1. How many grams of ammonia can be produced from the reaction of 1.8 moles of

nitrogen with excess hydrogen as shown below?

1 N2(g)

+

3 H2(g)

1.8 mol N 2 x

2 NH3(g)

2 mol NH3 17.04 g

x

= 61 g NH3

1 mol N 2

1 mol

Mole

Ratio

Molar

Mass

2. How many moles of hydrogen gas are required to produce 75.0 g of ammonia?

75.0g NH3 x ??????? x ??????? =

mol H2

3. How many moles of ammonia can be produced from the reaction of 125 g of

nitrogen as shown above?

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Chemistry 65

Chapter 8

STOICHIOMETRIC CALCULATIONS

Mass-Mass Calculations:

? Relates mass of reactants and products in a balanced chemical equation

Examples:

1. What mass of oxygen will be required to react completely with 96.1 g of propane,

C3H8, according to the equation below?

1 C3H8 (g) + 5 O2 (g)

96.1 g C3H8 x

3 CO2 (g) + 4 H2O (g)

1 mol C3H8

5 mol O2

32.00 g O2

x

x

= 349 g O2

44.11 g C3H8 1 mol C3H8

1 mol O2

Molar

Mass

Mole

Ratio

Molar

Mass

2. What mass of carbon dioxide will be produced from the reaction of 175 g of propane, as

shown above?

175 g C3H8 x ??????? x ??????? x ??????? =

5

g CO2

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